1. Field of Invention
The present invention relates to high-speed data communications cables using at least two twisted pairs of wires. More particularly, it relates to bundled cables including a plurality of individual cables bundled together.
2. Discussion of Related Art
High-speed data communications media often include pairs of wire twisted together to form a balanced transmission line. Such pairs of wire are referred to as twisted pairs. One common type of conventional cable for high-speed data communications includes multiple twisted pairs that may be twisted and bundled (cabled) together to form the cable. In addition, several individual cables are often twisted and bundled together to provide a bundled cable to facilitate installation. Two common types of cable that are often used in communications applications are unshielded twisted pair (UTP) cable and shielded twisted pair (STP) cable.
Communication cables must meet electrical performance characteristics required for transmission at high frequencies. The Telecommunications Industry Association and the Electronics Industry Association (TIA/EIA) have developed standards which specify specific categories of performance for cable impedance, attenuation, skew and crosstalk isolation. When twisted pairs are closely placed, such as in a cable, electrical energy may be transferred from one pair of a cable to another. Such energy transferred between pairs is referred to as crosstalk and is generally undesirable. The TIA/EIA have defined standards for crosstalk, including TIA/EIA-568A. The International Electrotechnical Commission (IEC) has also defined standards for data communication cable crosstalk, including ISO/IEC 11801. One high-performance standard for 100 Ω cable is ISO/IEC 11801, Category 5, another is ISO/EC 11801 Category 6.
In conventional cable, each twisted pair of a cable has a specified distance between common points of a twist along the longitudinal direction, that distance being referred to as the pair lay. When adjacent twisted pairs have the same pair lay and/or twist direction, they tend to lie within a cable more closely spaced than when they have different pair lays and/or twist direction. Such close spacing may increase the amount of undesirable crosstalk which occurs between adjacent pairs. Therefore, in some conventional cables, each twisted pair within the cable may have a unique pair lay in order to increase the spacing between pairs and thereby to reduce the crosstalk between twisted pairs of a cable. Twist direction may also be varied.
When two or more individual cables are bundled together to form a bundled cable, each individual cable, and the overall bundled cable, must meet the performance and, if plenum-rated, plenum standards discussed above. In order to save costs and simplify manufacturing of the bundled cable, a simple scheme to facilitate meeting the above requirements is desirable.